Not applicable.
Not applicable.
This invention relates generally to projection display systems, such as may be used in color televisions, business projectors, and computer displays, and more particularly to color scrolling systems used in conjunction with a light modulator.
Light pipes are used for homogenizing the output of a lamp in projection display systems to provide uniform illumination to a spatial light modulator(s) (xe2x80x9cSLMxe2x80x9d), but may be used in other applications where it is desired to expand light from a relatively small source into a larger field of uniform illumination. In color projection display systems, the white light from the lamp is separated into primary colors, red, green, and blue, with each color being modulated, either with separate modulators or with a sequential modulator, to create the color display.
One technique uses a rotating color wheel to sequentially scroll a series of red, green, and blue color filters across the exit face of the light pipe. The sequence of colors is provided to a display in rapid succession so that a human eye perceives a full color image. Unfortunately, as each color filter passes over the exit face of the light pipe, the non-transmitted colors are lost, either absorbed or reflected by the filter. Thus, the light from the light source is not efficiently used.
A further technique recaptures non-transmitted light by using a color wheel with a series of color filters that reflect the light not transmitted through the color filter. The input face of the light pipe is reflective to the wavelengths of interest, except for a clear aperture through which light from the lamp is coupled to the light pipe. Light reflected off the color wheel travels back through the light pipe, reflects off the input face, and travels back to the exit face. This process may occur several times until a different colored filter is present at the exit face, and the re-circulated light is transmitted through this filter. This process is called color recapture or color recycling.
However, this technique, while recapturing some of the light and thus improving efficiency, introduces additional loss mechanisms. First, the aperture can limit the light captured from the lamp, and allows light to be lost back through the aperture during the recapture sequence. If a reflective coating on the input face is not required, than the entire input face can be clear to couple all the incident light falling upon it into the light pipe. Second, the light pipe-air and air-color wheel interfaces can both introduce reflective losses. Third, if the color wheel is not flat when the light is reflected back into the light pipe, a portion of the light might exit the light pipe because of the change in the angle of incidence violates total internal reflection (xe2x80x9cTIRxe2x80x9d). Other losses, such as absorptive and scattering losses, can also occur. More importantly, if the color wheel is not flat, i.e. the distance between the color wheel and the light pipe changes during a revolution, the amount of light coupled back into the rod varies, leading to intensity variations at the spatial light modulator.
Therefore, it is desirable to provide color recapture systems without the aforementioned problems arising in systems employing color wheels.
A scrolling color system includes a color-separating light integrator and scrolling beam diverter. The color-separating light integrator could be a light pipe with two or more dichroic filters on the exit face, for example. Broad-spectrum light entering the light integrator is separated into light beams having selected color. The non-selected light from each filter is reflected back into the integrator for homogenization, thus efficiently using the light from the light source.
In another embodiment of the present invention, a color-separating recirculating light integrator also includes polarization recovery and recirculation. In yet another embodiment, a recirculating light integrator compensates for spatial brightness distribution at the light valve or display screen.